<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="./box.css">
    <!-- <script>
        document.getElementById("demo").innerHTML = "hello"
    </script> -->
</head>

<body>
    <!-- <input type="button" value="按钮" onclick="alert('hello')" value="我是一个按钮"> -->
    <div class="box1">
        <div class="box2">
            <div class="box3"></div>
            <div class="box4"></div>
        </div>
    </div>

</body>

</html>